This invention relates to a circuit arrangement for igniting and operating gas discharge lamps having a choke coil arranged between the lamp and the a.c. supply source and having an inductance L and an ignition device connected to the lamp. A capacitor having a capacitance C is connected in parallel with at least a part of the choke coil in order to obtain an ignition current that is higher than the normal lamp operating current.
In the operation of gas discharge lamps, problems frequently occur during the ignition process. This ignition process comprises three stages, i.e. a primary ionization of the discharge path, designated as breakdown, a subsequent low-current glow discharge between the lamp electrodes and the succeeding passage from the flow discharge to the actual high-current arc discharge. A frequently occurring cause of ignition difficulties is then a non-stable passage from the glow discharge to the arc discharge. In lamps having, for example, an amalgam filling, such as sodium high-pressure lamps filled with an Na/Hg amalgam, in the event of an unfavourable amalgam distribution in the discharge vessel, the discharge is applied to the amalgam instead of to the electrodes. As a result, the passage from the glow discharge to the arc discharge is made more difficult and the lamp remains in the glow stage, i.e. the ignition has failed. Similar problems arise with the re-ignition of still hot lamps. In this case, the effect frequently occurs that the passage from the glow discharge to the arc discharge takes place transiently, i.e. for a small part of an a.c. half cycle and then a change-over is effected again to a glow discharge.
By means of so-called heterodyne igniters, cold gas discharge lamps can be reliably ignited and still hot lamps can be readily reignited (see DE-OS Nos. 3108547 and 3108548 as well as U.S. Pat. No. 3,944,876). These known ignition circuits produce ignition pulses between 2 and 5 kV and 7 and 15 kV, respectively. The use of these circuits as external igniters for discharge lamps, which are to be provided, for example as an alternative to incandescent lamps with an E-27 cap, is not possible because the permissible voltage values prescribed for the E-27 cap are exceeded. Therefore, this application makes it necessary to accommodate the ignition circuits in the lamp base. However, this is made more difficult by the fact that the required capacitors are comparatively large and hence make it more difficult to obtain a compact lamp construction. Moreover, in the circuits according to the said DE-OS, even when they are accommodated in the lamp base, under given operating conditions voltages may still occur between the cap contacts which exceed the permissible values for the E-27 cap. Furthermore, with the use of the known ignition circuits in sodium high-pressure lamps at an elevated sodium pressure for improving the colour properties, it has been found that a direct restarting of the hot lamps, especially at a low mains voltage (198 V) is not possible, but that a certain time period elapses, which is not acceptable with the use of such lamps in many fields of application, more particularly, for example, in the domestic field.
It is further known from DE-PS No. 622171 and U.S. Pat. No. 3,890,537 to cause the lamp to be acted upon by a considerably increased starting current in order to improve the starting properties--more particularly in order to avoid an excessively long glow stage. This increased current flow takes place at least for about a mains half cycle, but mostly even for a considerably longer time. In the case of a choke coil, such an increased current can flow through a path parallel to the choke, whose a.c. impedance is comparable with or smaller than that of the choke. If this parallel path is constructed with a correspondingly large capacitor, the passage from the glow discharge to the arc discharge is improved, it is true, but at the subsequent zero passages reignition difficulties are met, which lead to extinguishing of the lamp. This appears from a lecture delivered during the "Third International Symposium on the Science and Technology of Light Sources" in Toulouse from 18 to 21 April 1983 by Mr. van Vliet about "Ignition of gas discharge lamps", in which the circuit arrangement mentioned in the opening paragraph was disclosed, in which the choke coil is shunted by a resistor or a large capacitor.